This invention relates to correcting for the resistance fluctuations in electric motor windings.
When electric motors are run in voltage mode, changes in the resistance of the windings result in changes in current for any given voltage. Because torque is directly proportional to current, such resistance fluctuations cause undesirable fluctuations in motor torque. The most common cause of resistance fluctuation in electric motors is heat.
Disclosed is an apparatus and method for adjusting a modeled resistance used in the control of an electric motor drive to match the actual resistance of the motor. The system comprises sensors for measuring motor current and motor speed, which data is inputted into a processing unit. The processor uses the measured rotational speed to calculate what the proper current should be based upon the torque desired. If the calculated current is not equal to the measured current, then the modeled resistance in the controller is altered to correct the current. The invention is particularly useful for permanent magnet brushless motors operating in voltage mode.